This invention relates to improved methods for treating organic acid-treated phosphatides. More particularly, this invention relates to improved methods that comprise the steps of providing a phosphatide-containing material obtained from organic acid refining of vegetable oil, adjusting the pH of the phosphatide-containing material to form a neutralized phosphatide, and drying the neutralized phosphatide for a time sufficient to produce a dried phosphatide containing hydrolyzed lecithin.
Phosphatides are one of several byproducts recovered during the purification of vegetable oil. Vegetable oils are typically obtained by pressing or extracting the oil seeds of plants such as corn or soybeans. Vegetable oils primarily consist of triglycerides, also termed triacylglycerols. In addition to triglycerides, however, vegetable oils also contain several other compounds. Some of these additional compounds, such as mono- and di-glycerides, tocopherols, sterols, and sterol esters, need not necessarily be removed during processing. Other compounds and impurities such as phosphatides, free fatty acids, odiferous volatiles, colorants, waxes, and metal compounds negatively affect taste, smell, appearance and storage stability of the refined oil, and hence must be removed. Carefully separated, however, some of these additional compounds, particularly the phosphatides, are valuable raw materials.
Vegetable oil triglycerides are esters of 1,2,3-propane triol, and can be represented by the generic formula 
where R1, R2, and R3 are the same or different, and are selected from the group consisting of C10-C22 saturated and unsaturated fatty acids. In soybean oil in particular, the saturated fatty acids that can occur include but are not limited to lauric (C12:0), myristic (C14:0), palmitic (C16:0), stearic (C18:0), arachidic (C20:0), and behenic (C22:0) acids. Generally, however, the fatty acids of soybean oil are predominantly unsaturated, and include but are not limited to oleic (C18:1), linoleic (C18:2), and linolenic (C18:3) acids. Unsaturated fatty acids can exist as geometric and/or positional isomers, each such isomer having different properties such as melting point. Naturally occurring fatty acids generally exist in the cis form, but they can be converted into the trans form during the course of purification steps used to produce a vegetable oil from an oilseed. Crude soybean oil in particular typically contains from about 95 to about 97 percent by weight triglycerides.
The terms phosphatides and phosphatide concentrates are commonly used to refer to a mixture of phospholipids comprising phosphatidyl derivatives which are present in crude vegetable oil. Such phosphatides also are referred to as gums. After being removed from vegetable oil by treatment with water, phosphatides are often called wet gums or wet lecithin. Upon being dried, phosphatides generally are termed lecithin or commercial lecithin. Crude soybean oil in particular provides the chief source for commercial lecithin.
The term lecithin, from a true chemical sense, refers to phosphatidyl choline. However, as used by commercial suppliers, the term lecithin refers to a product derived from vegetable oils, especially soybean oil. Specific chemical components of phosphatides present in vegetable oil include phosphatidyl choline, 1; phosphatidylethanolamine, 2; phosphatidylinositol, 3; phosphatidyl serine, 4; phosphatidic acid, 5; cyclolipids, and other components such as free sugars, metals and free fatty acids. 
Such phosphatides are amphipathic, i.e. one end of the molecule is hydrophilic (lipophobic) and the other end is hydrophobic (lipophilic). As a result, they possess useful surface-active properties, and can orient in aqueous environments to create membranes and bilayers.
The fatty acid content of the phosphatides 1 through 5 is represented by R1 and R2, as defined above, and generally matches that of the vegetable oil from which the phosphatides are derived. The phosphatide content of vegetable oil will vary based on a number of factors, including but not limited to oilseed type, seed quality, and the process by which oil is extracted therefrom. Crude soybean oil in particular typically contains from about 1.5 to about 3 percent by weight phosphatides. Phosphatides comprise both hydratable phosphatides (HPs) and non-hydratable phosphatides (NHPs). Although non-hydratable phosphatides tend to remain oil-soluble and are largely unaffected by water, hydratable phosphatides when hydrated become greater in density than the triglycerides and precipitate, or settle out. This phenomenon forms the basis for the process of conventional water degumming, discussed more fully below.
Lecithin varies in appearance from highly viscous to semiliquid to powder, and generally is brown in color. Hydrolyzed lecithin, also termed lysolecithin or lysophosphatidylcholine (LPC), is a desirable modified form of lecithin and generally comprises a highly viscous or pasty fluid ranging in color from light brown to brown. The composition of several lecithins derived from vegetable oil is shown in Table 1. The fatty acid composition of lecithin derived from soybean oil in particular is shown in Table 2.
Commercial lecithin is typically produced in a continuous process by drying phosphatide concentrates, which are obtained as byproducts of vegetable oil purification processes, at a temperature of from 176xc2x0 F. to 203xc2x0 F. and at an absolute pressure of from about 50 mm Hg to about 300 mm Hg. Erickson, David R., Degumming and Lecithin Processing and Utilization, in Practical Handbook of Soybean Processing and Utilization 174, 179-80 (David R. Erickson ed. 1995); Van Nieuwenhuyzen, W., J. Amer. Oil Chem. Soc. 53:425 (1976). However, processing lecithin at high temperature risks increasing the concentration of objectionable volatile compounds, and further risks permanently fixing these objectionable compounds to the lecithin via chemical bonding.
Vegetable oil impurities are typically removed in four distinct steps of degumming, refining, bleaching, and deodorizing. Of these four steps, degumming removes the largest amount of impurities, the bulk of which are hydratable phosphatides. Refining primarily removes non-hydratable phosphatides, soaps created from the neutralization of free fatty acids, and other impurities such as metals. Bleaching then improves the color and flavor of refined oil by decomposing peroxides and removing oxidation products, trace phosphatides, and trace soaps. Soybean oil bleaching materials include neutral earth (commonly termed natural clay or fuller""s earth), acid-activated earth, activated carbon, and silicates. Deodorizing is the final processing step and prepares the oil for use as an ingredient in many edible products including salad oils, cooking oils, frying fats, baking shortenings, and margerines. The deodorizing process generally comprises passing steam through refined oil at high temperature and under near vacuum conditions to vaporize and carry away objectionable volatile components.
Vegetable oil refining, also known as neutralization or deacidification, essentially involves removing free fatty acids (FFA) and phosphatides from the vegetable oil. Most refining operations employ either alkali refining (also termed caustic refining) or physical refining (also termed steam refining). Of these two refining methods, alkali refining predominates.
For either refining method, an optional but preferred first step is a conventional water degumming process. Degumming refers to the process of removing hydratable phosphatides and other impurities such as metals from vegetable oils. A simple degumming process comprises admixing demineralized water with the vegetable oil and separating the resulting mixture into an oil component and an oil-insoluble hydrated phosphatides component (frequently referred to as a xe2x80x9cwet gumxe2x80x9d or xe2x80x9cwet lecithinxe2x80x9d). The NHPs, generally considered to be calcium and magnesium salts of phosphatidic acids, are largely unaffected by water and remain soluble in the oil component. Phosphatidic acids are typically produced via the action of phospholipidases, which are released from the oil seed upon damage to the cellular structure.
Normally, refiners also must introduce chelating agents following degumming processes to remove metal compounds from crude vegetable oil, which typically contains calcium, potassium, magnesium, aluminum, iron and copper. Left in place, these metal impurities form salts of phosphatidic acid, thereby contributing to the NHP content. Moreover, metal contaminants, especially iron, can darken oil during deodorization, and even small amounts of iron that do not affect the oil""s color can nevertheless dramatically reduce stability of refined oil.
Treating crude vegetable oil with demineralized water produces a degummed oil and a phosphatide concentrate containing the hydratable phosphatide fraction. This phosphatide concentrate subsequently can be removed from the degummed oil by a convenient method such as by gravitational force or by centrifugal separation. Phosphatide concentrates coming from centrifugal separation will generally contain up to about fifty percent by weight water, and typically will contain from about twenty-five to about thirty percent by weight water. In order to minimize chances of microbial contamination, phosphatide concentrates must be dried or otherwise treated immediately. Dried phosphatide concentrates can be profitably sold as commercial lecithin. Degummed oil is further refined to remove NHPs and other unwanted compounds.
Mineral acid also is sometimes added during the water degumming process to help minimize the NHP content of degummed oil. The acid combines with calcium and magnesium salts, enabling phosphatidic acids to migrate from the oil to the water phase, thus eliminating them from the crude oil. However, using mineral acid during degumming is inappropriate when seeking to recover gums intended for use as lecithin because the presence of mineral acid will cause darkening of the lecithin.
In alkali refining, free fatty acids and gums are removed from crude or degummed oil by mixing the oil with a hot, aqueous alkali solution, producing a mixture of so-called neutral oil and soapstock (also termed refining byproduct lipid), which is an alkaline mixture of saponified free fatty acids and gums. The neutral oil is then separated from the soapstock, typically by centrifugation. The soapstock has commerical value due to its fatty acid content but must be processed further in order to render it salable. The neutral oil is further processed to remove residual soap.
Soapstock is treated in a process called acidulation, which involves breaking or splitting the soap into separate oil and aqueous phases through addition of a mineral acid such as sulfuric acid to reduce the pH to approximately 1.5, followed by thorough heating and mixing. Because the aqueous phase is heavier than the oil phase, the acidulated soapstock is separated from the oil by gravity or centrifugation. The separated oil (termed acid oil) has essentially the composition of the neutral oil and is drawn off, washed with water to completely remove mineral acid and sludge, and sold, usually as an animal feed supplement. The remaining aqueous phase (termed acid water) is the final waste product and must be neutralized before being discarded.
The alkali refining process has several drawbacks, however. One drawback is that alkali refining allows recovering only the hydratable phosphatide fraction, because the non-hydratable phosphatide fraction is destroyed and converted into materials that wind up in the soapstock. And although employing mineral acids during water degumming can reduce the overall NHP content prior to alkali treatment by converting the NHPs into water-soluble forms, thus potentially increasing the percentage recovery of the overall phosphatide fraction, using mineral acids during degumming causes undesirable darkening of lecithin.
An alternative to alkali refining is physical refining. Physical refining is a steam distillation process essentially the same as that used in conventional vegetable oil deodorization processes, in which steam passing through vegetable oil vaporizes and carries away free fatty acids. The main advantage of physical refining over alkali refining is that no soapstock is generated. A second advantage is lower refining losses because there is no saponification of oil and no oil entrainment and/or emulsification by soapstock.
Accordingly, there is significant interest in physical refining due to its economic advantages and friendliness compared to alkali refining. But because physical refining does not remove NHPs, any oils to be physically refined must be free of NHPs in order to ensure stable refined oils. Oils such as palm oil and tallow, which have low NHP content, can be successfully physically refined. But oils such as soybean oil and sunflower seed oil, which are relatively high in NHPs, are not commonly physically refined because the pre-refining step of water degumming does not remove NHPs. Moreover, physically refined soybean oils have only limited acceptance in the U.S. market due to their lack of flavor stability.
One recent and attractive alternative route to obtaining phosphatide-containing mixtures is organic acid refining of vegetable oil, as disclosed in pending U.S. patent application Ser. No. 09/197,953. In an organic acid refining process, a dilute aqueous organic acid solution is admixed with a heated stream of crude vegetable oil to give an acid-oil blend. The acid-oil blend is thereafter subjected to high shear for a time sufficient to finely disperse the dilute aqueous organic acid solution in the crude vegetable oil and give an acid-and-oil mixture (also termed a phosphatide-containing mixture) and/or is subjected to low shear for a time sufficient to produce a phosphatide-enriched aqueous phase (also termed a hydrated impurities phase) into which oil contaminants are sequestered and also produce a purified vegetable oil phase.
Vegetable oils suitable for organic acid refining include but are not limited to those derived from soybean oil, corn oil, cottonseed oil, palm oil, peanut oil, rapeseed oil, safflower oil, sunflower seed oil, sesame seed oil, rice bran oil, coconut oil, canola oil, and mixtures thereof. A particularly preferred vegetable oil is soybean oil.
The dilute aqueous organic acid solution may be prepared from any food grade organic acid, including but not limited to phosphoric acid, acetic acid, citric acid, tartaric acid, succinic acid, or combinations thereof. A particularly preferred organic acid is citric acid. Using a food grade organic acid, as opposed to a mineral acid, ensures that phosphatides removed during the purifying process can be purified and sold as commercial lecithin to the food industry. Using an organic acid also enables sequestering metal contaminants without the need to add other chelating agents. In preparing the dilute aqueous organic acid solution, demineralized water is preferably used. Using demineralized water avoids the possibility of converting hydratable phosphatides to non-hydratable phosphatides. As used herein, the term demineralized water means water substantially devoid of calcium and magnesium ions.
The dilute aqueous organic acid solution has a concentration based on the combined weight of organic acid and water of from about 1 to about 5 percent by weight. The dilute aqueous organic solution is combined with the heated vegetable oil in a ratio of from about 3:97 to about 20:80, depending on the source from which the vegetable oil is derived and on whether the vegetable oil has been degummed.
The phosphatide-containing mixture generally comprises hydratable phosphatides, nonhydratable phosphatides that have been converted into water-soluble form, water, organic acid, and vegetable oil, as well as other contaminants including but not limited to metals. The phosphatide-containing mixture is mixed at low shear for a time of less than about 16 minutes to allow sequestering of contaminants, especially metals, into the phosphatide-enriched aqueous phase. The term sequestering as used herein refers to the process wherein contaminants are either directly or indirectly (through chemical conversion into water-soluble forms) taken up into the phosphatide-enriched aqueous phase.
In one mode of organic acid refining, the phosphatide-containing mixture is separated into its component parts in a stepwise fashion, the first step of which is separation into two streams comprising a purified vegetable oil phase and a phosphatide-enriched aqueous phase. Separation can occur by any convenient method, including by centrifugation or by permitting the phosphatide-containing mixture to settle for a time sufficient to develop a purified vegetable oil phase and a phosphatide-enriched aqueous phase. This route can be employed because the purified vegetable oil typically separates fairly quickly from the phosphatide-enriched aqueous phase. The purified vegetable oil phase can be further processed, as for example by bleaching and deodorizing, and subsequently used or sold. The phosphatide-enriched aqueous phase can be dried or it can undergo further processing.
The phosphatide-enriched aqueous phase itself comprises an aqueous organic acid phase and an organic acid-treated phosphatide phase. Accordingly, a second separation step can be used to isolate one of these two remaining phases from the other. Once isolated, the aqueous organic acid phase can be recycled without further treatment into the organic acid refining process. The organic acid-treated phosphatide phase can be further processed.
In another mode of organic acid refining, the phosphatide-containing mixture is separated directly into three component parts comprising a purified vegetable oil phase, an organic acid-treated phosphatide phase, and an aqueous organic acid phase. Separation advantageously occurs by permitting the phosphatide-containing mixture to remain unagitated for a time sufficient to develop discrete phases. Typically, the purified vegetable oil phase migrates to the top, the organic acid-treated phosphatide phase migrates to the middle, and the aqueous organic acid phase migrates to the bottom. Once discrete phases exist, they can be separated from each other in any order. Typically, however, the purified vegetable oil phase is separated first, and then one of the two remaining phases is separated from the other. As above, the purified vegetable oil phase can be further processed, as for example by bleaching and deodorizing, and subsequently used or sold. The aqueous organic acid phase can be recycled without further treatment into the organic acid refining process. The organic acid-treated phosphatide phase can be further processed.
Thus, alternate modes of organic acid refining produce either a phosphatide-enriched aqueous phase or a more concentrated organic acid-treated phosphatide phase, which, alone or in combination, can be further processed to produce lecithin. Lecithins are utilized in a broad variety of applications and perform an array of valuable functions. In edible compositions, lecithin contributes nutritional value and also can act as an emulsifying agent, surface-active agent, anti-spattering-agent, or stabilizing agent. Lecithin can be used in technical applications as an anti-foam agent, dispersing agent, wetting agent, stabilizing agent, and as an anti-knock compound for gasoline formulations. In particular, in foods such as baked goods or margarine, lecithin is used as a dispersing agent, emulsifier, viscosity reducer and antioxidant. In cosmetics such as shampoos or skin lotions, lecithin is employed as a foam stabilizer, emollient, emulsifier, and wetting agent. In pharmaceuticals targeted for either topical or parenteral administration, lecithin functions as softening agent, carrier, emulsifier, and penetration enhancer. Lecithin also possesses unique release properties, and is useful in pan-frying and pan grease formulations for baking, as well as in mold release formulations which enable casting forms to be easily removed.
If mistreated during drying, however, lecithin can have an objectionable odor and flavor that is difficult to remove. Phosphatides easily oxidize when subjected to heating, and such oxidative products can contribute a bitter or rancid taste to lecithin. Heating of phosphatides can also induce formation of volatile decomposition products such as 4,5-dimethylisoxazole, which contributes an objectionable flavor to lecithin. Other volatile compounds such as isophorone, a contributor of objectionable odor, can form by an aldol condensation reaction involving solvent remaining from crude vegetable oil refining processes. Thus, care must be exercised in the method used to remove objectionable volatile components from lecithin.
Changes in lecithin functionality and physicochemical properties can be made using various modification techniques. For example, fractionating lecithin in ethanol changes the ratio of phosphatidylcholine to phosphatidylethanolamine to produce a material having improved oil-in-water emulsifying ability. Acetytlation using acetic anhydride also improves oil-in-water emulsifying ability. Hydroxylation using hydrogen peroxide and lactic acid or a peracid improves oil-in-water emulsifying ability and water dispersibility. Hydrolysis of lecithin, normally achieved either via action of strong base or acid or via enzymatic action, provides a material having improved hydrophilic and emulsifying properties. Enzymatically modified lecithins incorporated into animal feed formulations can improve emulsification and digestibility of fats. In some animal studies, such hydrolyzed lecithins, also termed lysolecithins, were shown to be more rapidly absorped following oral administration.
A typical acidic hydrolysis process for producing hydrolyzed lecithin comprises multiple processing steps of adding water and an acid such as hydrochloric acid to a dried lecithin, subsequently neutralizing with a base such as sodium hydroxide, and then redrying the lecithin. J. C. Schmidt and F. T. Orthoefer, Modified Lecithins, in Lecithins 203, 206 (Bernard F. Szuhaj and Gary R. List eds., 1985). However, such a process is inefficient because it requires drying, then rewetting, and then redrying. Moreover, because the most desirable hydrolyzed lecithin results when only one fatty acid is cleaved from the glyceride backbone, hydrolysis reactions employing strong acid or base can prove difficult to control in terms of halting the reaction at a desired point.
A typical enzymatic process for producing hydrolyzed lecithin comprises adding enzymes to a wet lecithin to catalyze conversion of the lecithin into a hydrolyzed lecithin. However, such enzymes are costly, and are often animal-derived, which can affect consumer acceptance. Moreover, enzymatic processes for producing hydrolyzed lecithin require that the enzymes be filtered out after lecithin conversion, adding further expense.
Thus, previously known methods for obtaining hydrolyzed lecithin have required complex and expensive processing steps. Consequently, further improvements in obtaining hydrolyzed lecithin have been sought. The present invention relates to improved processes having advantages over those previously disclosed. Surprisingly, the processes of the invention produce hydrolyzed lecithin directly and simply from either a phosphatide-enriched aqueous phase or an organic acid-treated phosphatide phase, both of which are obtained from an organic acid refining process.
One aspect of the present invention relates to an improved process that produces a dried phosphatide containing hydrolyzed lecithin from a phosphatide-containing material selected from the group consisting of a phosphatide-enriched aqueous phase obtained from an organic acid refining process, an organic acid-treated phosphatide phase obtained from an organic acid refining process, or a mixture thereof.
Another aspect of the invention relates to an improved process that produces a lecithin containing hydratable phosphatides and non-hydratable phosphatides that have been converted into water-soluble form. This aspect of the invention maximizes recovery of the overall phosphatide fraction contained in crude vegetable oil.
One embodiment of the invention is a process for treating an organic acid-treated phosphatide that comprises the steps of providing a phosphatide-containing material selected from the group consisting of a phosphatide-enriched aqueous phase obtained from an organic acid refining process, an organic acid-treated phosphatide phase obtained from an organic acid refining process, or a mixture thereof; adjusting the pH of the phosphatide-containing material to a value of from about 5 to about 7 to form a neutralized phosphatide mixture; and drying the neutralized phosphatide mixture for a time sufficient to convert the neutralized phosphatide mixture into a vapor phase and a dried phosphatide containing hydrolyzed lecithin.
Another embodiment of the invention is a process for treating an organic acid-treated phosphatide that comprises the steps of providing a phosphatide-containing material selected from the group consisting of a phosphatide-enriched aqueous phase obtained from an organic acid refining process, an organic acid-treated phosphatide phase obtained from an organic acid refining process, or a mixture thereof; adjusting the pH of the phosphatide-containing material to a value of from about 5 to about 7 to form a neutralized phosphatide mixture; drying the neutralized phosphatide mixture for a time sufficient to convert the neutralized phosphatide mixture into a vapor phase and a dried phosphatide containing hydrolyzed lecithin; and discharging the dried phophatide at a temperature of less than about 150xc2x0 F.
Yet another embodiment of the invention is a process for treating an organic acid-treated phosphatide that comprises the steps of providing a phosphatide-containing material selected from the group consisting of a phosphatide-enriched aqueous phase obtained from an organic acid refining process, an organic acid-treated phosphatide phase obtained from an organic acid refining process, or a mixture thereof; adjusting the pH of the phosphatide-containing material to a value of from about 5 to about 7 to form a neutralized phosphatide mixture; bleaching the neutralized phosphatide mixture; and drying the neutralized phosphatide mixture for a time sufficient to convert the neutralized phosphatide mixture into a vapor phase and a dried phosphatide containing hydrolyzed lecithin.
Still another embodiment of the invention is a process for treating an organic acid-treated phosphatide that comprises the steps of providing a phosphatide-containing material selected from the group consisting of a phosphatide-enriched aqueous phase obtained from an organic acid refining process, an organic acid-treated phosphatide phase obtained from an organic acid refining process, or a mixture thereof; allowing the phosphatide-containing material to remain at acidic pH for a time of no more than about 8 hours; adjusting the pH of the phosphatide-containing material to a value of from about 5 to about 7 to form a neutralized phosphatide mixture; and drying the neutralized phosphatide mixture for a time sufficient to convert the neutralized phosphatide mixture into a vapor phase and a dried phosphatide containing hydrolyzed lecithin.
Still another embodiment of the invention is a process for treating an organic acid-treated phosphatide that comprises the steps of providing a phosphatide-containing material selected from the group consisting of a phosphatide-enriched aqueous phase obtained from an organic acid refining process, an organic acid-treated phosphatide phase obtained from an organic acid refining process, or a mixture thereof; allowing the phosphatide-containing material to remain at acidic pH for a time of no more than about 8 hours; adjusting the pH of the phosphatide-containing material to a value of from about 5 to about 7 to form a neutralized phosphatide mixture; bleaching the neutralized phosphatide mixture; and drying the neutralized phosphatide mixture for a time sufficient to convert the neutralized phosphatide mixture into a vapor phase and a dried phosphatide containing hydrolyzed lecithin.
These and other aspects of the invention will become apparent in light of the detailed description below.